This invention relates to a gas-insulated bus bar which comprises:
a case filled with electric insulation high pressure gas;
a bus conductor supported in the case substantially coaxially therewith; and
a support arm which is positioned between the bus conductor and case to support the bus conductor in such a manner that said bus conductor extends substantially axially of the case. The above-mentioned type of gas-insulated bus bar is already known.
FIG. 1 shows a cross section of the prior art gas-insulated bus bar. A metal cylindrical case 10 usually electrically grounded is filled with an electric insulation high pressure gas such as sulfur hexafluoride (SF.sub.6). A metal pipe bus conductor 12 is securely held in the substantially cross sectional center of the case 10 by a plurality (three in FIG. 1) of support arms 14 which are connected at one end to the bus conductor 12 and at the other end to the case 10 substantially equidistantly in the circumferential direction of the case 10. The support arm 14 comprises an embedded metal member 14a welded or airtightly screwed to the inner peripheral wall of the case 10 and an electrically insulating support rod 14b, in the outer end portion of which the embedded metal member 14a is cast.
The conventional gas-insulated bus conductor 12 constructed as described above is generally supposed to have the drawbacks that the bus conductor 12 is excessively elongated relative to the case 10 in accordance with changes in ambient temperature or in the heated condition of the various parts of the bus conductor 12 itself; the resultant bending load causes the support arms 14 to be more extended to undergo an axial stress; and consequently the support arms 14, particularly mechanically weak electrically insulating support rods 14b are likely to be broken; and said breakage of the support rods 14b gives rise to objectionable events such as a decline in the electric insulating property of a gas-insulated bus bar and consequently a decrease in the power-transmitting property of the entire power transmission line using such defective bus bar.